Grommets are available from the dealer or a lot of other places. They are cheap. Remove panel in trunk. Remove power lead from antenna. Remove two screws that hold antenna and lower it out of the hole. Remove old grommet. New grommet will be easier to work with if you warm it up in pan of hot water. Fit it into hole in fender and be sure to get the rubber lip seated all the way around. Be sure you have nice round opening when looking down through installed grommet. I like to put just a dab of silicon grease on the "ball" part of the antenna before I put it backl in place. Seems to make it fit easier and maybe fill any tiny spaces that could hold water. I figure to gave to replace teh grommet on any Benz I buy. 15 minutes work.